Procedure and system for ensuring emergency communication

ABSTRACT

The present invention relates to data communication networks. In particular, the present invention relates to a procedure and a system for ensuring successful emergency communication in a data communication network in which the terminal devices (4a, 4c) are connected to the local exchange via an access node (3) consistent with the V5 standard. In the procedure of the invention, in the event of a failure of the V5 interface used by a subscriber, the subscriber&#39;s emergency traffic is directed to emergency lines created locally in the access node. The emergency line is optionally connected to a specified location, such as the teleoperator&#39;s customer service.

The present invention relates to data communication networks. Inparticular, the present invention relates to a procedure as defined inthe preamble of claim 1 and to a system as defined in the preamble ofclaim 9 for ensuring emergency communication in an access node connectedto a data communication network and having a number of subscriber linesor subscribers connected to it for the connection of terminal equipmentto the data communication network. Furthermore, the present inventionrelates to a procedure for the testing of the emergency communicationfeature, as defined in the preamble of claim 7.

There are at least two commonly known methods for connecting subscribersto an exchange in a data communication network. In the first method, thesubscriber is connected via a subscriber line directly to the exchangeor to an access module connected to it. In the second method, thesubscriber is connected to an access network, whose access node isconnected to the exchange. Open interfaces (V5.1 and V5.2) between anaccess network and a local exchange are defined in the ETSI (EuropeanTelecommunications and Standards Institute) standards of the ETS 300 324and ETS 300 347 series. V5 interfaces enable subscribers belonging to aphysically separate access network to be connected to a telephoneexchange using a standard interface. A dynamic concentrator interfaceV5.2, consistent with the standards ETS 300 347-1 and 347-2, consists ofone or more (1-16) PCM (Pulse Code Modulation) cables. One PCM cablecomprises 32 channels, each of which with a transfer speed of 64 kbit/s,i.e. 2048 kbit/s in all. The V5.2 interface supports analogue telephonesas used in the public telephone network, digital, such as ISDN(Integrated Services Digital Network) basic and system connections aswell as other analogue or digital terminal equipment based on semi-fixedconnections.

A static multiplexer interface V5.1, consistent with the standards ETS300 324-1 and 324-2, consists of one PCM cable with a transfer speed of2048 kbit/s. The V5.1 interface supports the same subscriber types asthe V5.2 interface, except for the ISDN system connection.

The terminal equipment can be connected to the access ports of theaccess node. One or more V5 interfaces can be connected to an accessnode. The access ports are created in the V5 interface by linking anunambiguous address of each port with a given address of the V5interface. In the local exchange, this address is created as a V5subscriber. In other words, each access port has an address which islinked with a V5 address and uses a given time slot or given time slotsfor signalling to the local exchange.

The purpose of a system for ensuring emergency communication is to makesure that calls to emergency numbers of subscribers connected to anaccess node can be set up even when the V5 interface between the accessnode and the exchange is out of order. The V5.1 and V5.2 standardscontain no definition of systems for ensuring emergency communication incase of failure. In this situation, the problem is that, at present, allcommunication, including emergency communication, via a specific V5interface of a given subscriber is hindered when the V5 interface fails.

One possibility for ensuring emergency communication in case of failureof a V5 interface assigned to a subscriber is to create in the telephoneexchange to which the V5 interface is connected a separate emergencyaddress for each subscriber for communication during the failuresituation. However, the problem with this system is the high capacityrequired in the exchange, because in this case the exchange must have adouble subscriber address range as compared with the number ofsubscribers. In addition, such an arrangement would significantlyincrease the size of the interface database of the access node.

The object of the present invention is to eliminate the problemsdescribed above. A specific object of the invention is to present aneffective procedure for ensuring emergency communication in an accessnode in the event of a failure of the V5 interface used by a subscriber.A further object of the present invention is to present a featurecurrently missing in the access node that makes it possible to ensuresubscribers' emergency communication as long as the access node is inoperation.

As for the features characteristic of the invention, reference is madeto the claims.

In the procedure of the present invention for ensuring emergencycommunication in a data communication network comprising a number oftelephone exchanges interconnected via trunk cables and an access nodeconnected to at least one of the exchanges, a number of terminal devicesused by subscribers to set up connections over the data communicationnetwork are connected to the access node, preferably via subscribercables. Further, in the procedure of the invention, signallingconsistent with the V5 standard, which is defined in the standardsmentioned above, is used in the connection between the access node andthe telephone exchange, which is a standard V5 interface.

In the procedure of the invention, an emergency line is created in theaccess node by using local operation control commands. The emergencyline is generally created in conjunction with the installation andstart-up of the access node. In this application, `emergency line` meansan access node subscriber line to which emergency communication isdirected when the link between the access node and the local exchange isbroken. Emergency communication is preferably controlled by using theinternal group switch of the access node. Further, at least oneemergency number is created for the emergency line of the access node byusing local access node commands. In the event of a failure of the V5interface used by a terminal device, a call from the terminal device toan emergency number is connected locally by means of the internal groupswitch of the access node. In the access node, the control of emergencylines and numbers in a failure situation is effected using MML (ManMachine Language) commands.

As compared with prior art, the present invention has the advantagethat, using the procedure of the invention, emergency communication ofsubscribers connected to an access node can be effectively and reliablyguaranteed even in the event of a failure of the V5 interface used bythe subscriber.

In a preferred embodiment of the present invention, when a newconnection is being set up, the status of the V5 interface used by thesubscriber is monitored in the access node, and if, based on thismonitoring, the V5 interface is found to be out of order, apredetermined connection setup mode is entered in which the connectionis set up locally in the access node. In a preferred case, at themonitoring stage, the status of the V5 interface used by the subscriber,i.e. information as to whether the interface is in working order or not,is read from a file used to store status data relating to each V5interface, i.e. data indicating failure and restoration of the controlchannel of the V5 interface. A failure situation in a V5 interfaceoccurs when the signalling connection from the subscriber to the localexchange fails.

In a preferred embodiment, the emergency line is connected via apermanent link to a location predetermined by the teleoperator, such asan exchange room, the teleoperator's customer service or the like. Inaddition, a permanent link can be provided from the emergency line to amobile telephone, a pager or equivalent. When the teleoperator receivesvia a data network supervision system or equivalent a message aboutmalfunction of one or more V5 interfaces in an access node, service canbe provided via the emergency line connected to the exchange room. Inpractice, this means that a terminal device connected to the emergencyline is attended by a human operator, and calls made to emergencynumbers by subscribers connected to the cranky V5 interface will producea ring in this terminal device and the subscribers can communicate theiremergency message via this line. If the call to the emergency numberfails to be set up, the subscriber is given a corresponding notice, asound signal or the like, informing the subscriber about the problem intelephone traffic.

The invention also relates to a procedure for testing the operation ofemergency lines and/or emergency numbers created in an access node. Thetesting procedure is used to ensure that emergency communication via theaccess node really works. In the testing procedure of the invention, atleast two emergency lines are provided in the access ride, so that aconnection to an emergency number can be set up from one of theemergency lines. The signalling programmes automatically perform a checkto see whether the V5 access port calling an emergency number has a V5address and whether the calling line has been created as an emergencyline for failure situations. If it is established in the access nodethat the call setup message to an emergency number comes from anemergency line of the access node, then the access node will work in amanner corresponding to operation in a failure situation and the call isconnected to the dialled emergency number. Further, if the connectionsetup to the emergency line is successful, this is an indication thatthe emergency communication feature is operational. Further, aconnection can be set up from the emergency lines in both directions, inother words, first from the first emergency line to the second one andthen from the second emergency line to the first one, thus making surethat both emergency lines are in working order. A further advantage ofthe checking procedure is that the emergency lines can be tested withoutinterrupting normal telephone traffic through the access node.

Further, in the system of the invention for ensuring emergencycommunication in a data network comprising a number of telephoneexchanges interconnected via trunk cables and an access node which isconnected to at least one of the exchanges and to which are connected anumber of terminal devices used by subscribers to set up connectionsover the data communication network, signalling according to the V5standard is used in the connection between the access node and thetelephone exchange, which is a V5 interface consistent with the V5standard. According to the invention, the access node comprises anemergency line created using the local operation control commands of theaccess node and an emergency number created using the local operationcontrol commands of the access node, and calls to the emergency numberare connected to the emergency line. Moreover, the access node of theinvention comprises means, preferably an internal group switch withinthe access node, which group switch is preferably a fully digital,full-scale single-phase time-shared switch without rejection, by whichcalls made by subscribers to emergency numbers are directed to theemergency line when the V5 interface used by the subscriber is out oforder.

In the following, the invention is described by the aid of a fewexamples of its embodiments by referring to the attached drawing, inwhich

FIG. 1 presents a prior-art signalling arrangement for a normal callover a V5 interface;

FIG. 2 presents a system according to the present invention; and

FIG. 3 represets a signalling arrangement in an access node for a callto an emergency number according to the present invention.

FIG. 1 presents an example of the signalling in the case of a prior-artISDN call over a V5 interface. When the subscriber picks for theheadphone (step 1), LAPD signalling (data link layer protocol in ISDNchannel D) is started. The access node (AN) 3 activates the terminaldevice (step 2) and sends a message indicating activation of theterminal device to the telephone exchange (LE) 1 (step 3), using thecontrol protocol. Once activated, the terminal device 4c sends a SETUPmessage over channel D of the subscriber cable. On receiving the SETUPmessage, the access node identifies (step 5) the corresponding V5interface and the V5 subscriber address of the subscriber cable (whichin fact is a third-layer address, L3 address, consistent with the OSIarchitecture (Open System Interconnection)) on the basis of thesubscriber cable. Moreover, the access node adds a V5 header to theSETUP message and sends it via the Ds channel of the corresponding V5interface to the telephone exchange 1. The LAPD signalling itself ispassed as such over the V5 interface via the signalling channel reservedfor the subscriber. Thus, the V5 interface software in the access node 3does not interfere with the contents of messages in any way. In thetelephone exchange 1, the V5 header is removed (step 6) and the SETUPmessage is transmitted further to an ISDN call setup control stage,where it is terminated. Based on the first SETUP message, the localexchange selects the V5 time slot to be used, and this information isgiven to the access node 3 together with the L3 address (step 7). Theaccess node 3 identifies the subscriber cable on the basis of the L3address received and, via its local group switch, connects (step 8) theB channel of the subscriber cable to the V5 interface time slot reservedfor it. Further, the access node 3 sends (step 9) to the telephoneexchange 1 a message confirming completion of the connection. Thetelephone exchange 1 sends the standard ISDN call control messagesrelating to call setup to the terminal device via the access node overthe Ds channel reserved for the subscriber cable (step 10).

The system presented in FIG. 2 comprises an access node 3 with a numberof subscribers 4a, 4c connected to it. The access node 3 operatesbetween an exchange 1 and the subscribers 4a, 4c and connectssubscribers to a telephone exchange in a data communication network inthe manner illustrated by FIG. 1. The access node 3 is connected via aV5.2 interface 5, which comprises 1-16 PCM cables (2 Mbit/s), to theexchange terminal (ET) 10 of the terminal exchange 1, which is providedwith the functions required by the V5 interface. The access node canalso be connected to the telephone exchange 1 via a V5.1 interface. Toensure successful emergency communication, the access node comprises atleast one emergency line 6 created for emergency communication andconnected to a specified terminal device via a connection preferablycarried out by an operator. A number of emergency numbers are created inthe access node 3. For each emergency number, preferably one or moreemergency lines are created. Due to the requirements pertaining to theaccess node, generally no other numbers except emergency numbers arecreated in it.

In the access node 3, one emergency number at a time can be created andfor each emergency line 6, one to six emergency numbers can be created.When the emergency lines are being created, the lines are given with alogical location number so that the command gives the access modulenumber only once, because the series attribute of the emergency numbersin a preferred embodiment is limited to one access module. From theseries attribute being limited to one access module it alsoautomatically follows that all emergency lines under a given emergencynumber must be included in the same access module. In an embodiment, itis possible to create a maximum of 20 emergency numbers for oneemergency line, yet the total number of emergency numbers is preferablynot more than 20. Moreover, the maximum length of an emergency number is12 digits. Further, an emergency number cannot be created as a normalsubscriber line, and on the other hand a normal subscriber cannot beassigned a line created as an emergency line.

In a preferred embodiment of the present invention, the maximum numberof emergency calls that can be active at the same time is 4, whichdepends on the number of emergency lines. In a further embodiment, thepush-button dialling receiver of the access node limits the number ofanalogue emergency calls at the setup stage to 64. It must be noted,however, that if the subscriber uses pulse dialling, the push-buttondialling receiver is released immediately at the beginning of thedialling, permitting a larger number of emergency calls at the setupstage. In the case of digital emergency calls, no push-button diallingreceiver is needed.

Next, referring to FIG. 3, the call setup procedure in the case of anISDN call to an emergency number according to a preferred embodiment ofthe invention will be described. The program modules presented in thesignal chart 3 are used as follows. MB1PRB is a program used for thetransmission of LAPD frames, which maintains specific information aboutthe routing direction of signalling in each port and performs theconnection of time slots in the access module. PRLPGM is an ISDN 2^(nd)-layer programme for access node failure situations, which monitors thecondition of the Ds channel of the V5 interface and reports changes inthe status of the interface. IS3PRS is an ISDN 2^(nd) -layer programmefor access node failure situations, which allocates a module cable foran ISDN subscriber. CDNPRB takes care of actual call setup in emergencycommunication, connection and disconnection of the speech path,connection of messages and reservation and release of push-buttondialling receivers. SWICOP is a progamme controlling the local groupswitch 7 of the access node. ZASPRB takes care of analogue subscribersignalling. An outgoing ISDN (2B+D) emergency call in the event of afailure of the V5 interface used by the subscriber is as follows. Whenthe subscriber picks up the headphone to call an emergency number, LAPDsignalling (data link layer communication protocol in ISDN channel D) isstarted by the MP1PRB module. IS3PRB acknowledges the activationrequest. Next, 2-layer connection consistent with the OSI model is setup by means of the PRLPGM and IS3PRB modules. Call setup is now started,and at this point the procedure differs from normal ISDN call setup; asthere is no connection to the local exchange, no V5 interface header isincluded in the message. Further, module IS3PB checks that the requiredparameters are in order. When the subscriber dials a number it isanalyzed by the appropriate programme to establish whether thesubscriber is calling an emergency number existing in the access nodeconcerned. If the call is found to be addressed to such an emergencynumber, then the call setup procedure is continued and the subscriber isgiven the necessary sound signals to indicate that the system is tryingto set up a connection to the emergency number. When the emergencynumber responds, i.e. when the called subscriber picks up the headphoneor performs some other action to answer the calling subscriber's callattempt, a talking connection is set up.

A call setup process as described above can also be carried out from anemergency line created in the access node by making a call from it to anemergency number. This makes it possible to test the emergency lines tomake sure that the emergency lines and the access node control systemfor calls to local emergency numbers are in working order.

Let it be further noted that, in call setup in a failure situation, theemergency line busy test, number analysis and call termination can becarried out in the access node in many known ways, as can the call setupprocess described above. It should be further noted that the exampledescribed above can also be applied to environments other than ISDN,e.g. an analogue environment.

The invention is not restricted to the examples of its embodimentsdescribed above, but many variations are possible within the frameworkof the inventive idea defined by the claims.

I claim:
 1. Procedure for ensuring emergency communication in a datacommunication network comprising comprising a number or telephoneexchanges interconnected via trunk cables and an access node connectedto at least one of the exchanges, to which access node are connected anumber of terminal devices used by subscribers to set up connectionsover the data communication network, in which procedure signallingaccording to the V5 standard is used in the connection between theaccess node and the telephone exchange, which connection is an accessnode V5 interface consistent with the V5 standard, characterized inthat, in the event of a failure of the V5 interface used by a terminaldevice, a call from the terminal device to an emergency number isconnected locally to an emergency line created beforehand in the accessnode.
 2. Procedure as defined in claims 1, characterized in thatwhen anew connection is being set up, the status of the V5 interface used bythe terminal device is monitored in the access node; and if, based onthis monitoring, the V5 interface is found to be out of order, apredetermined connection setup mode is entered in which the connectionis set up locally in the access node.
 3. Procedure as defined in claim1, characterized in that data relating to the status of each V5interface, i.e. data indicating failure and restoration of the controlchannel of each V5 interface, is stored in a specific file in the accessnode.
 4. Procedure as defined in claim 1, characterized in that thestatus data stored in a specific file for each V5 interface is utilizedwhen a new connection is being set up.
 5. Procedure as defined in claim1, characterized in that the emergency line is connected via itpermanent link to a location predetermined by the teleoperator, such asan exchange room, the teleoperator's customer service or the like. 6.Procedure as defined in claim 1, characterized in that, if theconnection fails to be set up, the subscriber is given a correspondingnotice, a sound signal to the like.
 7. Procedure for testing theoperation of a procedure as defined in claim 1, characterized inthatfrom one of two emergency lines created in advance, a connection isset up to an emergency number and the signalling programmes of theaccess node automatically perform a check to see whether the V5 accessport in question has a V5 address; a check is made to establish whetherthe calling line has been created as an emergency line for failuresituations; if a connection to the emergency line is successfully setup, this is an indication that the emergency lines are operational. 8.Procedure as defined in claim 7, characterized in that a connection isbe set up from the emergency lines in both directions, i.e. from thefirst emergency line to the second one and from the second emergencyline to the first one.
 9. System for ensuring emergency communication ina data network comprising a number of telephone exchanges (1, 1a)interconnect via trunk cables (2) and an access node (3) which isconnected to at least one of the exchanges and to which are connected anumber of terminal devices (4a, 4b, 4c) used by subscribers to set upconnection over the data communication network, in which systemsignalling according to the V5 standard is used in the connectionbetween the access node and the telephone exchange, which connection isan access node V5 interface (5) consistent with the V5 standard,characterized in that the access node comprisesan emergency line (6)created using the local operation control commands of the access node;an emergency number created using the local operation control commandsof the access node, and calls to the emergency number are connected tothe emergency line; and means (7) by which calls made by subscribers toemergency numbers are directed to the emergency line when the V5interface used by the subscriber is out of order.
 10. System as definedin claim 9, characterized in that the system comprises means (8)connected to the emergency line for setting up a connection to aspecified terminal device (4b) via the emergency line.